def fact(n):
    if n > 1:
        return n * fact(n - 1)
    else:
        return 1


if __name__ == '__main__':
    n = int(input("请输入一个非负正整数："))
    if n >= 0:
        print("运算结果：{0}！={1}".format(n, fact(n)))
    else:
        print("无效输入！")
